Currently, the use of contact lenses for the correction of visual acuity is well known. Contact lens is more convenient than eyeglasses for most occasions, therefore, it becomes more popular recently.
Astigmatism is a defect in the eye that is corrected by a lens with a non-spherical prescription. The prescription, which is usually expressed as cylinder on the patient's prescription order, causes at least a portion of the surface of the lens to have an oval shape. Such lenses are called toric lenses. Nowadays, toric lenses are used for correction of the wearers astigmatism. The corrective lens must be properly oriented with respect to the eye of the wearer. That is, the intended top of the lens must be at the top of the wearer's eye. For ordinary glasses this presents no problem, because the lens is permanently fixed to the frame at the correct rotational orientation. The ear and nose pieces of the frame assure that the frame and the lens do not rotate with respect to the wearer's eyes. For contact lenses orientation is subject to constant alteration. In the case of contact lenses whose function is to correct astigmatism this is unacceptable.
Some of the toric lenses are oriented with the lens' thickness differential. However, these toric lenses are disadvantageous in that they rely on the interaction of the eyelid margin and the lens' thickness differential to orient an axis alignment of the toric lens on the wearer's eye. As the thickness of the lens increases in the optical area of the lens, the lens becomes thicker and heavier so as to make the user uncomfortable.
Therefore, there is a need to correct the axis alignment of the contact lens without increasing the thickness of the contact lens in the optical area thereof.